The present invention relates to a gas spring and particularly to an improved gas spring for a rear door of a vehicle, for example.
Various proposals have been made for gas springs for rear doors of vehicles. In a gas spring of this type, a rod body is inserted into a cylinder body. The rod body is movable in and out of the cylinder body, but is urged in a direction outwardly of the cylinder body by the pressure of a gas sealed inside the cylinder body. The spring thus assumes an extended configuration when no external force is acts on the spring.
When such a gas spring is used on the rear door of a vehicle, the spring is extended when the rear door is open, and the door is kept open so long as no outside force is applied to the door. If, on the other hand, there is an unexpected external force such as the wind, for example, the rear door may close suddenly and unexpectedly. There have thus been proposals for gas springs that include lock mechanisms to maintain the gas springs in their extended configurations. One such spring is described, for example, in Japanese Patent Application Publication No. 2007-64281.
That gas spring, which includes a rod body that is inserted into and movable in an out of a cylinder body, also has a cylindrical body that forms a part of a cover body. The cover body is movable about a base end portion that is pivotally attached to a distal end portion of the rod body where the rod body projects outside of the cylinder body. The distal end portion of the rod body lies adjacent to a head end portion of the cylinder body.
The distal end portion of the cover body has a stopper member that forms a part of the lock mechanism. The stopper member holds the head end portion of the cylinder body inside it, and moveable in a direction perpendicular to the cylinder body as the cover body moves. When the stopper body is moved forward in a first direction, the stopper body interferes with the head end portion of the cylinder body and thereby stops the rod body's movement into the cylinder body. When the stopper body is moved backward in the other direction, the interference with the head portion of the cylinder body is no longer present and contraction of the rod body into the cylinder body is once again allowed.
The gas spring described in the Japanese patent application publication thereby allows a user to lock the spring in place by moving the stopper body with respect to the cylinder body. When the gas spring is thus locked, the gas spring will remain extended and will not contract even if an unexpected external force such as that of the wind acts on the rear door, and the rear door will therefore not close unexpectedly.
The gas spring described in the Japanese application works well when the lock mechanism is acting normally, but may be less than ideal, though, in that the lock mechanism may be prone to a certain malfunction in long term use.
More specifically, in the gas spring described above, the lock mechanism's stopper member's movement with respect to the cylinder body is limited by a detent structure. If the detent structure stops functioning, the locked state of the locking mechanism will not be maintained.
In a gas spring of this type, the lock mechanism's stopper member is frequently formed of a synthetic resin material because such a material is inexpensive and easy to manufacture, and light in weight.
It may occur, though, that dust or sand adhered to the outside of the cylinder body may polish or abrade the projection that forms the detent structure as the stopper member moves back and forth over the detent. If the projection is abraded sufficiently, the detent structure will no longer be effective and the lock mechanism will not function as intended.
There is a further possible problem, in that dust or fine sand adhering to the outside of the rod body that moves in and out of the cylinder body may also adhere to a lip portion of the dust seal at the head end of the cylinder body. That foreign material may scratch the outer surface of the rod body, which may allow the gas sealed inside of the cylinder body to leak out of it.